Electic potential on a cone

Thanks for taking the time to look at this. I'm getting ready to go to grad school, and I'm realizing that although I did ok in my classes, there are large gaps in my knowledge of physics. That said, I'm currently trying to work my way through an E&M book, and now I'm stuck.

Here's the problem

Pretend that you have an open ended cone with the vertex at the origin and the fat end a distance located at a height R. Coincidently, the Radius of the cone at this height is also R. This cone also carries a uniform surface charge sigma. Find the potential difference between the vertex of the cone and the point at the center of the its base.

Try setting up the integrand using cylindrical coordinates [tex](r, \theta, z)[/tex] since that is an obvious choice for cylindrical symmetry (note: you can also use spherical coordinates...they might seem more logical at first sight).